#include <stdio.h>
int main()
{
    int a, b, c;
    char mark;
    scanf("%d%d%d", &a, &b, &c);
    if (a != b && a != c)
        mark = 'A';
    if (a != b && b != c)
        mark = 'B';
    if (a != c && b != c)
        mark = 'C';
    printf("%c", mark);
    return 0;
}